Such a probe head is described, for example, in U.S. Pat. No. 3,869,799. It belongs to the category of so-called "measuring" probe heads, which emit a signal proportional to the deflection of the probe carrier, as opposed to so-called "switching" probe heads, which only generate a pulse-shaped signal at the instant of contact with the workpiece.
The measuring force generators of the known probe head are plunger coil systems mounted in the upper part of the probe head so that the waste heat generated during operation is kept away as much as possible from the guide units configured in the manner of a spring parallelogram, from which the flexible probe carrier is suspended. A rod assembly is used for the transmission of forces applied by the plunger coils to the spring parallelograms assigned to the individual coordinate directions; this makes the force transmission indirect and "soft". The spring parallelograms can also be fixed in the individual coordinate directions by means of mechanical catches which arrest the deflections of the spring parallelograms in their electrical or mechanical zero points.
In this probe head, it is difficult to systematically set the measuring forces and the fixation in other than the directions mechanically defined by the spring parallelograms.
In German Patent 3,210,711, another probe head of the "measuring" type is described. In this probe head, the measuring force generators are located directly on the guide units for the different deflection directions also implemented in the form of spring parallelograms. An electronic system is associated with the probe head via which the direction of the force vector can be set at will according to pregiven desired values. In addition, passive damping elements are assigned to the individual guide unit directions, which prevent uncontrolled oscillation of the flexible probe about its zero position. However, this known probe head does not permit the flexible probe carrier to be clamped in individual coordinate directions.
From U.S. application Ser. No. 08/035,716, filed Mar. 23, 1993, now U.S. Pat. No. 5,471,406, a probe head is known which can be clamped electronically by applying strong restoring forces to the drives in the probe head upon probe deflection. The configuration of the probe head is not described in detail.
From German published patent application 4,001,981, it is known to dampen the vibrations of the horizontal arm of a stationary coordinate measuring apparatus by adding mass at the side of the probe head, either by using a viscous liquid in which the additional mass moves, or actively with the help of a drive for the additional mass and a control device which activates the drive in dependence upon signals of a vibration sensor. This, however, is only sufficient to keep the probe head at rest, but does not dampen the relative movement between the flexibly mounted probe and the part of the probe head which is permanently connected to the housing.
In addition, the previously mentioned probe heads all have a relatively complicated and hence expensive mechanical configuration, partly because separate, additional assemblies are used for clamping and damping. These assemblies are not very flexible with respect to the setting of clamping forces and damping characteristics and cannot easily be adapted to varying operating conditions or measuring tasks.